Chromium iron oxide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2020-08-04 to 2021-02-17

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to same study

Objective of study:

absorption

other: lung clearance

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 413 (90-day (Subchronic) Inhalation Toxicity Study)

Version / remarks:

2018-06-25

Deviations:

yes

Remarks:

Ophthalmology not performed (this endpoint is not sensitive in particle studies); urine analysis not performed (endpoint optional in guideline).

GLP compliance:

yes (incl. QA statement)

Remarks:

GLP certificate signed 2018-11-22.

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: at room temperature, dry, protected from light.

Radiolabelling:

no

Species:

rat

Strain:

Wistar

Remarks:

Crl:WI (Han)

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany
- Females nulliparous and non-pregnant: yes
- Age at study initiation: approx. 8 weeks
- Weight at study initiation: approx. 280 g for males and approx. 180 g for females
- Housing: housed in Makrolon (polycarbonate) cages type III with softwood (‘ssniff KB 8-15’) bedding material.
- Diet (ad libitum): commercial chow in pellet (ssniff “V1534”; supplier: ssniff Spezialdiäten GmbH, Soest, Germany).
- Water (ad libitum): tap water
- Acclimation period: approx. one week the animals will be allowed to adjust and become acclimatised to the Fraunhofer ITEM environment. During the 2 - 3 weeks prior exposure start, all rats will be trained to the 6-hour restraint in nose-only tubes.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2
- Humidity(%): 55 ± 15
- Photoperiod (hrs dark/light): 12 / 12

Route of administration:

inhalation: aerosol

Vehicle:

unchanged (no vehicle)

Remarks:

filtered air

Details on exposure:

TYPE OF INHALATION EXPOSURE: nose only

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: flow-past nose-only inhalation exposure system
- Method of holding animals in test chamber: restrain tubes with a flexible stopper.
- System of generating particulates/aerosols: the particulate sample aerosols were generated by dry dispersion with pressurized air. Cyclones (in line) were used to reduce the coarse moiety of the aerosol. For each nose-only exposure unit, the aerosol was generated by a high-pressure pneumatic disperser. The disperser was fed with the test/reference items under computerized control, i.e. with a feed back loop to the actual aerosol concentrations measured by an aerosol photometer. The photometer gives a scattering light signal which is proportional to the particle concentration, if the particle size distribution is constant. The ratio between photometer signal and concentration was determined throughout the study by comparing to gravimetric concentrations.
- Temperature, humidity, pressure in air chamber: parameters were recorded by 20-minute means The were set at 22°C + 2°C for temperature and 55% + 15% for relative humidity.
- Air flow rate: 1 L/min.
- Method of particle size determination: the MMAD was determined four times (once before exposure start and once per month during the exposure period for each test item exposure unit (3 units) by a cascade impactor (Marple impactor).
- Treatment of exhaust air: exhaled air is drawn off immediately by a cylinder surrounding the aerosol delivery cylinder.

TEST ATMOSPHERE
- Brief description of analytical method used: filter samples of the aerosols were taken daily to control the aerosol concentrations and to calibrate the aerosol photometers. The means are close to the target concentrations.
- Samples taken from breathing zone: yes

Duration and frequency of treatment / exposure:

13 weeks (65 exposure days); 6 hours/day, 5 days/week

Dose / conc.:

0.6 mg/m³ air (analytical)

Remarks:

SD: ± 0.09 mg/m³; 0.1 mg/lung (calculated total dose using MPPD v3.04)

Dose / conc.:

2.5 mg/m³ air (analytical)

Remarks:

SD: ± 0.35 mg/m³; 0.4 mg/lung (calculated total dose using MPPD v3.04)

Dose / conc.:

10.02 mg/m³ air (analytical)

Remarks:

SD: ± 1.49 mg/m³; 1.7 mg/lung (calculated total dose using MPPD v3.04)

No. of animals per sex per dose / concentration:

15 males: 5 males (1 day recovery); 5 males (28 days recovery); 5 males (90 days recovery)

Control animals:

yes, concurrent vehicle

Positive control reference chemical:

none

Details on study design:

- Dose selection rationale: concentrations were defined based on the preceding intratracheal instillation dose range finding (DRF A) study (Fraunhofer ITEM no. 02 N 20 502).
- Post-exposure recovery period: 1, 28, and 90 days

The nominal aerosol concentrations of 0.6, 2.5 and 10 mg/m³ were selected to achieve lung burden at the highest concentration that is at or above the lung overload conditions, i.e. impaired lung clearance. The test item deposition in the respiratory tract was modeled using the MPPD model (version 3.04), resulting in a deposited fraction of 4.7% (rel. density=5.1, MMAD/GSD=1.8 µm/1.5).
This deposited fraction was used to calculate the total deposited mass, using the following input parameters:
Morphometry: Semi-symmetric Long Evans
Example for deposited mass at 0.6 mg/m³: 0.2 l minute breathing volume x 360 min exposure/day x 65 exposure days x 0.6 mg/m³ x 4.7% = 0.13 mg/lung
Example for deposited mass at 2.5 mg/m³: 0.2 l minute breathing volume x 360 min exposure/day x 65 exposure days x 2.5 mg/m³ x 4.7% = 0.55 mg/lung

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption)
- Tissues and body fluids sampled: lungs
- Time and frequency of sampling: 1, 28, and 90 days after the 90-day exposure period

ANALYTICAL METHOD
- Complete description including:

lungs of 5 male rats in all exposure groups were subjected to a chemical analysis to verify the predicted retained mass of the test items after 90 days of inhalation +1; +28 and + 90 recovery days. For recovery days +1 and +28 whole lungs were available. On +90 days the right lung lobe was available for analysis. Here a conversion factor of 1.67 was applied to extrapolate the lung burden to the whole lung. Between animal sacrifice and sample preparation samples were stored at -20 °C. Prior to microwave digestion lung tissue samples underwent a freeze-drying step (approx. 48 h), followed by plasma ashing (approx. 48 h, cool plasma conditions). H2SO4 (1 mL) and HNO3 (4 mL) were added to sample in a quartz glass vial and subjected to a microwave digest (max. 500 W). Samples were left to cool down and transferred into PP tubes before adding HF (1 mL). After 16 h the sample volume was made up to 50 mL with deionised water. After appropriate dilution (see raw data) with deionised water samples were analyzed by ICP-MS. In the case of HF having been added during the digest H3BO3 was added during sample dilution (see raw data). Quantification was achieved against matrix matched standards. To ensure validity of the analysis data, samples were bracketed by QC standards.

after sacrifice the lungs were prepared by freeze drying (> 6 hours (0.37 mbar), plasma ashing (> 24 hours, cool plasma conditions), and microwave (wet) digestion (1 mL H2SO4 (96%) and 4 mL HNO3; max. 500 W). Samples were left to cool down and transferred into PP tubes before adding HF (1 mL). After 16 h the sample volume was made up to 50 mL with deionised water. After appropriate dilution with deionised water samples were analyzed by ICP-MS. In the case of HF having been added during the digest H3BO3 was added during sample dilution. Quantification was achieved against matrix matched standards. To ensure validity of the analysis data, samples were bracketed by QC standards.

Parameter/Setting:
System: icap Q (ThermoScientific) or icap TQ in single quadrupole mode (ThermoScientific);
Autosampler: Cetac ASX 520 or ESI 4DX;
Interface: High matrix;
Mode: KED (Helium);
Plasma [W]: 1.550;
Spray chamber: Cyclonic;
Number of main runs: 5;
Analytes (m/z) (Qualifier; Quantifier): 52Cr; 53Cr;
Internal standards (m/z): Chromium: 45Sc; 74Ge.
Limit of quantification: 0.1 ng Cr/mL dilution

Statistics:

Differences between groups will be considered statistically significant at p < 0.05. Data will be analysed using analysis of variance. If the group means differ significantly by the analysis of variance, the means of the treated groups will be compared with the means of the control groups using Dunnett’s test. The statistical evaluation of the histopathological findings will be done with the two-tailed Fisher test by the PROVANTIS system.

Preliminary studies:

A dose range finding study by intratracheal instillation was conducted. For further information please refer to the study record in IUCLID section 7.2.4.

Type:

absorption

Results:

Lung burden with chromium iron oxide after 1, 28, and 90 days after the 90-day exposure period:
- 0.6 mg/m3: 141, 89 and 39 µg/lung;
- 2.5 mg/m3: 531, 341 and 225 µg/lung;
- 10.02 mg/m3: 1924, 1972 and 895 µg/lung.

Type:

other: lung clearance half-time

Results:

after exposure to 0.6 mg chromium iron oxide/m3 air: 49.5 days

Type:

other: lung clearance half-time

Results:

after exposure to 2.5 mg chromium iron oxide/m3 air: 81.5 days

Type:

other: lung clearance half-time

Results:

after exposure to 10.02 mg chromium iron oxide/m3 air: 80.6 days

Details on absorption:

For detailed information of absorption in lung tissue please refer to the filed "overall remarks, attachments".

Details on distribution in tissues:

not measured

Details on excretion:

not measured

Metabolites identified:

not measured

Enzymatic activity measured:

not measured

Bioaccessibility (or Bioavailability) testing results:

not measured

Conclusions:

Male rats were exposed to concentrations of 0.6, 2.5 and 10.02 mg chromium iron oxide/m3 air for 6 hours per day, 5 days/week for 90 days via nose-only inhalation. The lung burden and clearance with chromium iron oxide were determined 1, 28 and 90 days after the 90-day exposure period. A vehicle control group was run concurrently.

One day, 1 month and 3 months after end of exposure, in the low-dose groups 0.14, 0.09 and 0.04 mg/lung, in the mid-dose groups 0.53, 0.34 and 0.23 mg/lung, and in the high-dose groups 1.92, 1.97 and 0.90 mg/lung of the test item chromium iron oxide (Pigment 3) were determined, respectively. The retained masses correspond quite well to the theoretical data derived from the MMPD model prediction.
During the recovery period a retarded lung clearance was observed in the high-dose group. In contrary, in the mid- and low-dose groups a partial and a physiological lung clearance was found, respectively. This reflects well the different grade of clearance retardation due to the various lung loads.
The clearance half-times of the low concentration groups with 50 days was in the range to the physiological half-time of approx. 60 days (ECETOC, 2013), or 50.5 days (median over all 5 sub-chronic inhalation toxicity studies, low-dose animals). In the mid- and high-dose group, a half-time of 81 days was determined, being above a 1.5-fold increase as compared to the physiological values of 50.5 or 60 days. The concentration-dependent increase in clearance half-times is indicative for a poorly soluble low toxicity (PSLT) particle, which may lead to a lung overload condition, i.e. impaired clearance in which the deposited dose of inhaled PSLT in the lung overwhelms clearance from the alveolar region leading to a reduction in the ability of the lung to remove particles (Driscoll and Borm, 2020). Although the 2-fold increase in lung clearance half-time retardation has not been reached, it is assumed that chromium iron oxide still fulfils the criteria as being a PSLT and that additional concentration groups with higher exposure would not have yielded any other effects than local inflammation at presence of higher clearance-half time values.

Reference 2

Endpoint:

basic toxicokinetics in vitro / ex vivo

Remarks:

Bioaccessibility - transformation/dissolution in artificial physiological media

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-11-10 to 2010-02-10

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Objective of study:

other: Bioaccessibility

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

yes

Remarks:

Bioaccessibility testing: loading of 100 mg/L; five artificial physiological media agitated at 100 rpm, at 37 °C ± 2 °C; sampling after 2 h and 24 h; determination of Cr and Fe concentrations after filtration by and ICP-MS.

Principles of method if other than guideline:

Solubility of test item in simulated human fluids. Principle of test is similar to OECD Series on testing and assessment number 29 guidance document on transformation/dissolution of metals and metal compounds in aqueous media (2001; document ENV/JM/MONO(2001)9).

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2009-06-19

Species:

other: in vitro (simulated human body fluids)

Details on exposure:

Test principle in brief:
- five different artificial physiological media,
- single loading of test substance of ~100 mg/L,
- samples taken after 2 and 24 hours agitation (100 rpm) at 37 °C,
- two method blanks per artificial media were tested; measurement (ICP-MS) of dissolved Cr an Fe concentrations after filtration (0.45 µm, syringe filters)
- the study was performed in triplicates

The aim of this test was to assess the dissolution of Chromium iron oxide in five artificial physiological media: Artificial lysosomal fluid (ALF, pH = 4.5), Artificial sweat solution (ASW, pH = 6.5), Gamble´s solution (GMB, pH = 7.4), Artificial gastric fluid (GST, pH = 1.5), Phosphate buffered saline (PBS, pH = 7.4). The test media were selected to simulate relevant human-chemical interactions (as far as practical), i.e. a substance entering the human body by ingestion into the gastrointestinal tract and by inhalation.

Duration and frequency of treatment / exposure:

Samples were taken after 2 h and 24h.

Dose / conc.:

100 other: mg of the test item /L artificial media

Details on study design:

Reagents
Water, HPLC grade obtained from the Laboratory Water Purification System
- Standard solutions at pH 4.00, pH 7.00 and at pH 10.00 (Merck)
- Nitric acid 65 %, Suprapur (Merck)
- Sodium chloride, NaCl (Merck)
- Potassium choride, KCl (Merck)
- Dibasic sodium phosphate, NaH2PO4 (Sigma)
- Dibasic potassium phosphate, KH2PO4 (Merck)
- Urea (Merck)
- Lactic acid (Fluka)
- Ammonia solution 25% (NH4OH) aqueous (Merck)
- Magnesium chloride hexahydrate, MgCl2 x 6H2O (Merck)
- Sodium sulfate, NaSO4 (Merck)
- Calcium chloride dihydrate, CaCl2 x 2H2O (Merck)
- Sodium acetate trihydrate (Sigma)
- Sodium bicarbonate, NaHCO3 (Sigma)
- Sodium citrate dihydrate (SAFC)
- Sodium hydroxide, NaOH (Merck)
- Citric acid (Sigma)
- Calcium chloride, CaCl2 (Merck)
- Sodium phosphate heptahydrate, NaH2PO4 x 7H2O (Sigma)
- Glycerine (Merck)
- Sodium tartrate dehydrate (Sigma)
- Sodium lactate (Sigma)
- Sodium pyruvate (Sigma)
- Formaldehyde (Merck)

Reference Material
- Multi-element analytical standard solution at 100 mg/L (ppm) of chromium and iron supplied by Ultra Scientific (batch number: K00285, expiry date: 31/05/2012)

Inductively coupled plasma-mass spectrometer (ICP-MS), Agilent Technologies HP7500CX
The ICP-MS analysisi was performed as a non GLP test at "Theolab", a laboratory located in Volpiano (TO). Therefore, it was excluded from the GLP statement.
Calibration: 0.1 - 50.0 µg/L
Correlation coefficient > 0.99
LOQ: 1 µg/L
LOD: 0.5 µg/L

Details on dosing and sampling:

Loading:
The nominal loading in this test was 100 mg/L. However, due to weighing uncertainties the actual loadings range from 99.6 mg/L to 103.6 mg/L in the test vessels.

Type:

other: Bioaccessibility

Results:

Highest dissolution at a loading of 0.1 g/L in GST after 24 h: Cr: 1.2 ± 0.04 µg/L, Fe: 17.5 ± 0.4 µg/L

Analytical method (Inductively-Coupled-Plasma Mass-Spectrometry ICP-MS)

 

Specificity

Blanks from each test medium were analysed. Considering the diverse inorganic salt composition of each test medium, the concentrations of Fe and Cr metals in blanks of the respective media were different. It was observed that the media with the highest salt content (i.e. test media 4.5 and 7.4) had the highest concentrations of Fe and Cr.

 

Linearity and System Precision

The analysed range from 0.1 µg/L to 50 µg/L was found to be linear for Cr and Fe (correlation coefficient > 0.99 for either metal).

Since the fortification levels for the recovery test were 1 µg/L and 10 µg/L, the linear calibration performed for recovery quantification ranged from 0.1 µg/ L to 50 µg/L.

The instrumental limit of detection (I.D.L.) defined as the lowest calibration level, was 0.1 µg/L for Cr and Fe.

The limit of quantification (L.O.Q.) of the method was 1 µg/L for Cr and Fe, defined as the lowest fortification level.

The limit of detection (L.O.D.) of the method, defined as 50 % of the lowest fortification level, was 0.5 µg/L for Cr and Fe.

 

Repeatability (Precision) and Accuracy (Recovery)

For precision, the SANCO/3029/99 rev. 4 guideline requires an RSD to be lower than 20 % for all tested media and fortification levels; therefore the precision of the analytical method can be considered acceptable.

For accuracy, the SANCO/3029/99 rev. 4 guideline requires individual recovery values in the range from 70 to 110 % with a mean between 80 to 100 % for all tested media and fortification levels, therefore the accuracy of the analytical method can be considered acceptable.

Considering the low concentrations tested (low fortification level 1 µg/L and high fortification level 10 µg/L), the precision of the analytical method (fixed at 10 %) and the complexity of the aqueous matrices tested the accuracy of the analytical method can be considered acceptable.

From the data and results of the accuracy test it can be concluded that no matrix effect was observed and no contribution of the filter procedure was observed.

Recovery Cr

Test Media	Spike add	MeanFound	Test No.	Precision (RSD %)	Recovery
pH 1.5	1 µg/L	1.0 µg/L	L (3 det.)	2.6 %	99.7%
	10 µg/L	9.8µg/L	H (3 det.)	1.3 %	98.2 %
pH 4.5	1 µg/L	1.0 µg/L	L (3 det.)	7.1 %	103.0 %
	10 µg/L	10.8 µg/L	H (3 det.)	13.9 %	107.5 %
pH 6.5	1 µg/L	1.2 µg/L	L (3 det.)	1.8 %	116.7 % (*)
	10 µg/L	11.8 µg/L	H (3 det.)	4.1 %	118.0 % (*)
pH 7.2	1 µg/L	1.0 µg/L	L (3 det.)	2.9 %	100.5 %
	10 µg/L	10.3 µg/L	H (3 det.)	2.0 %	103.0 %
pH 7.4	1 µg/L	1.0 µg/L	L (3 det.)	1.3 %	99.3 %
	10 µg/L	9.9 µg/L	H (3 det.)	2.0 %	98.5 %

(*) Out values from the range of acceptability following guideline SANCO/3029/99 rev.4 but considering the precision of the analytical method fixed at 10 % it can be acceptable.

Recovery Fe

Test Media	Spike add	MeanFound	Test No.	Precision (RSD%)	Recovery
pH 1.5	1 µg/L	1.1 µg/L	L (3 det.)	2.8 %	113.5 % (*)
	10 µg/L	10.3 µg/L	H (3 det.)	7.7 %	103.3 %
pH 4.5	1 µg/L	0.8 µg/L	L (3 det.)	3.7 %	85.0 %
	10 µg/L	9.7 µg/L	H (3 det.)	11.9 %	96.6 %
pH 6.5	1 µg/L	1.1 µg/L	L (3 det.)	5.9 %	113.6 % (*)
	10 µg/L	11.7 µg/L	H (3 det.)	2.1 %	116.8 % (*)
pH 7.2	1 µg/L	1.1 µg/L	L (3 det.)	7.9 %	111.9 % (*)
	10 µg/L	10.2 µg/L	H (3 det.)	3.3 %	102.4 %
pH 7.4	1 µg/L	0.7 µg/L	L (3 det.)	3.6 %	74.6 %
	10 µg/L	10.1 µg/L	H (3 det.)	4.7 %	100.7 %

(*) Out values from the range of acceptability following guideline SANCO/3029/99 rev.4 but considering the precision of the analytical method fixed at 10 % it can be acceptable.

Summary results for ⁵²Cr

^52Cr(µg/L)		Artificial gastric fluid (pH 1.5)	Artificial lysosomal fluid (pH 4.5)	Artificial sweat solution (pH 6.5)	Phosphate buffered saline (pH 7.2)	Artificial interstitial fluid (pH 7.4)
Blank	Mean	n.d.	2.7	n.d.	n.d.	n.d.
	S.D.	-	0.1	-	-	-
	CV (%)	-	5.1 %	-	-	-
T2h	Mean	<1	n.d.	<1	<1	n.d.
	S.D.	-	-	-	-	-
	CV (%)	-	-	-	-	-
T24h	Mean	1.2	<1	<1	<1	n.d.
	S.D.	0.04	-	-	-	-
	CV (%)	3.4 %	-	-	-	-

n.d.: lower than the method Limit of Detection (L.O.D.) (0.5 µg/L for Cr)

Summary results for ⁵⁶Fe

^56Fe(µg/L)		Artificial gastric fluid (pH 1.5)	Artificial lysosomal fluid (pH 4.5)	Artificial sweat solution (pH 6.5)	Phosphate buffered saline (pH 7.2)	Artificial interstitial fluid (pH 7.4)
Blank	Mean	<1	18.4	n.d.	2.0	2.7
	S.D.	-	0.8	-	0.1	0.1
	CV (%)	-	4.3 %	-	5.7 %	4.0 %
T2h	Mean	7.5	1.4	1.5	<1**	<1**
	S.D.	0.4	0.1	0.3	-	-
	CV (%)	4.8 %	5.1 %	17.7 %	-	-
T24h	Mean	17.5	7.9	<1**	<1**	n.d.
	S.D.	0.4	0.4	-	-	-
	CV (%)	2.2 %	4.5 %	-	-	-

n.d.: lower than the method Limit of Detection (L.O.D.) (0.5 µg/L and Fe)

**: Lower than the method Limit of Quantification (L.O.Q.) (1 µg/L for Fe)

Conclusions:

The dissolution of chromium of the test item Chromium iron oxide is in most cases <1 µg/L or below the L.O.D at a loading of 0.1g/L after 2 and 24 hours. Only in artifical gastric fluid (pH 1.5) a low concentration of Cr (1.2 µg/L) after 24 hours is dissolved.
The dissolution of iron of the test item Chromium iron oxide is in a range of below the L.O.D. (pH 7.4) and 17.5 µg/L (pH1.5) at a loading of 0.1 g/L after 2 and 24 hours. A pH dependent dissolution can be observed.
As dissolved Cr and Fe concentrations were below 18 µg/L even at the highest loading of 0.1 g/L, referring to a solubility of < 0.018 %, the pigment is considered biologically inert.

Executive summary:

The bioaccessibility of Chromium iron oxide has been investigated experimentally in vitro by simulating dissolution under physiological conditions considered to mimic the most relevant exposure routes (oral, dermal and inhalation), as follows:

- Gamble’s solution (GMB, pH 7.4) which mimics the interstitial fluid within the deep lung under normal health conditions,

- Phosphate-buffered saline (PBS, pH 7.2), which is a standard physiological solution that mimics the ionic strength of human blood serum,

- Artificial sweat (ASW, pH 6.5) which simulates the hypoosmolar fluid, linked to hyponatraemia (loss of Na+ from blood), which is excreted from the body upon sweating,

- Artificial lysosomal fluid (ALF, pH 4.5), which simulates intracellular conditions in lung cells occurring in conjunction with phagocytosis and represents relatively harsh conditions and

- Artificial gastric fluid (GST, pH 1.5), which mimics the very harsh digestion milieu of high acidity in the stomach.

As dissolved Cr and Fe concentrations were below 18 µg/L even at the loading of 100 mg/L pigment, corresponding to a solubility of less than 0.018 %, the pigment, Chromium iron oxide, is considered biologically inert.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015-07-14 to 2015-07-17

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Objective of study:

toxicokinetics

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Version / remarks:

2010-07-22

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2014-05-14

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: at room temperature, kept dry, and stored in a tightly closed container

Radiolabelling:

no

Species:

rat

Strain:

other: Crl:CD(SD)

Details on species / strain selection:

The species was selected for this study design because the rat is a commonly used rodent species for toxicity studies.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Research Models and Services, Germany GmbH, Sandhofer Weg 7, 97633 Sulzfeld, Germany
- Age at administration: males: 54 days; females: 68 days
- Weight at administration: males: 268 - 297 g; females: 227 - 252 g
- Housing: kept singly in MAKROLON cages (type III plus) with a basal surface of approx. 39 cm × 23 cm and a height of approx. 18 cm; bedding material: granulated textured wood (Granulat A2, J. Brandenburg, 49424 Goldenstedt, Germany)
- Diet (ad libitum): certified commercial diet (ssniff® R/M-H V1534, ssniff Spezialdiäten GmbH, 59494 Soest, Germany)
- Water (ad libitum): drinking water
- Acclimation period: 6 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22°C ± 3°C (maximum range)
- Relative humidity: 55% ± 15% (maximum range).
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

other: chromium iron oxide: oral (gavage); reference item (chromium (III) acetate hydroxide): oral (gavage) and intravenously injected

Vehicle:

other: chromium iron oxide: 0.8 % aqueous hydroxyl propyl methylcellulose gel; reference item (chromium (III) acetate hydroxide): water (oral administration) or 0.9 % NaCl solution (intravenous administration)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
1) Chromium iron oxide
The test item was suspended in the vehicle to the appropriate concentration freshly on the administration day.

2) Reference item (chromium (III) acetate hydroxide)
The reference item was dissolved in the vehicle for oral/intravenous injection.

The administration formulations were continuously agitated by stirring throughout the entire administration procedure.
Administration volume (oral administration / intravenous administration): 10 mL/kg bw

Injection speed (intravenous adminsitration): dose per approx. 15 seconds

The amount of test item and reference item was adjusted to each animal's current body weight on the administration day.

Duration and frequency of treatment / exposure:

single administration

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose / concentration:

5 males / 5 females

Control animals:

no

Positive control reference chemical:

none

Details on study design:

- Dose selection rationale: the dose levels for this preliminary study had been selected after consultation with the Sponsor based on available toxicity data:
The oral LD50 value for the reference item was as follows:
chromium acetate, basic: >5000 mg/kg bw
Furthermore, oral bioavailabilities of soluble Cr(III) substances are given in the public domain with approx. 0.1 to 2%.

The test item oral dose of 1000 mg/kg bw corresponds to the limit dose used in a separate 28-day oral toxicity study, which is considered the maximum feasible dose. Based on the chemical composition of the test item, a dose of 1000 mg/kg bw of chromium iron oxide equates to a dose of 212.1 mg Cr/kg bw (corresponding to 820.2 mg Cr3(OH)2(CH3COO)7/kg bw).

The dosage for the reference item administered by intravenous injection was set to 10% of the dose of the reference item adminstered by oral administration on a stoichiometric basis for chromium, thereby lowering the dose for reasons of tolerability of the test animals. This equates to a dose of 21.21 mg Cr/kg bw (corresponding to 82 mg Cr3(OH)2(CH3COO)7/kg bw).

The dose levels for the reference item (oral and intravenous administration) were confirmed in two preliminary experiments each employing two animals per group:

1) First preliminary experiment
Both animals treated once orally with 820.2 mg chromium(III) acetate hydroxide/kg bw revealed slight pilo-erection starting approx. 15 minutes after administration lasting 4 hours.
Both animals treated once intravenously with 82 mg chromium(III) acetate hydroxide/kg bw revealed slight pilo-erection starting approx. 15 minutes after administration lasting 4 hours. Further, haemorrhagic urine was observed within approx. 15 minutes and 1 hour after administration.

2) Second preliminary experiment
Haemorrhagic urine was noted for the two animals treated once with an intravenous injection of 40 mg chromium (III) acetate hydroxide/kg bw at approx. 30 minutes after the administration. The condition of the urine had returned to normal at later checks.
No signs of systemic toxicity were observed for the two animals treated once orally with 400 mg chromium (III) actete hydroxide/kg bw.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: plasma
- Time and frequency of sampling: blood was collected 0 (predose), 1, 2, 4, 8, 12, 24, 48, and 72 hours after administration. The whole blood samples were cooled using an IsoTherm-Rack system until centrifugation. Immediately after centrifugation, the plasma was frozen at -80°C, and stored at this temperature until analysis.
In addition, 4 mL pooled blank plasma (approx. 2 mL per sex) were obtained from spare animals.

A toxicokinetic evaluation of the data on chromium iron oxide plasma levels will be performed. A non-compartment model will be employed. The following parameters will be determined:
AUC0-inf = extrapolated area from zero to infinity
AUC0-t last = extrapolated area from time zero to the last quantifiable plasma concentration >LLOQ
Kel = elimination rate constant
t½ = elimination half-life

Cmax values will be the highest measured plasma concentrations, and tmax values will be the time points of highest plasma concentrations.

Elimination rate constants (Kel) and plasma elimination half-lives (t½) will be calculated by linear regression analysis of the log/linear portion of the individual plasma concentration-time curves (c = concentration, t = time).

Area under the curve (AUC) values will be calculated using the linear trapezoidal method and extrapolated to infinite time by dividing the last measurable plasma concentration by the elimination rate constant. Plasma concentrations at time zero will be taken to be those at the first blood sampling time.

Furthermore, AUC0-t last-values will be calculated according to the linear trapezoidal rule. Values below or at the lower limit of quantification (LLOQ) will be excluded from the calculation.

OBSERVATIONS
- clinical signs: before and after dosing as well as regularly throughout the working day (7.30 a.m. to 4.30 p.m.) and on Saturdays and Sundays (8.00 a.m. to 12.00 noon; final check at approx. 4.00 p.m).
- mortality: early in the morning and again in the afternoon of each working day as well as on Saturdays and Sundays (final check at approx. 4.00 p.m).
- body weight: at the time of group allocation and on the administration day.

TEST ITEM FORMULATION ANALYSIS
The remaining administration formulations of each test and reference item that was mixed with a vehicle were stored at ≤- 20°C (approximately 5 mL per formulation, in total 3 samples).

Statistics:

The reference item-treated group (oral administration) was compared to the test item treated group.
The following statistical method was used:
STUDENT's t-test: body weight (p ≤ 0.01 and p ≤ 0.05)
The following limits were used:
p = 0.05 / 0.01 about t = 2.3060 / 3.3554
(for 8 degrees of freedom)

Preliminary studies:

Please refer to the field "Details on study design" above.

Type:

absorption

Results:

Cmax-levels in plasma of 0.16 μg Cr/g & 0.55 μg Cr/g & 3.44 μg Fe/g & 4.97 μg Fe/g were noted 0 to 72 h (tmax as range of both analytes m/f) after i.v. administration of 0.83 mg Chromium(III) acetate hydroxide/kg bw, for the m & f rats on day 1, resp..

Type:

absorption

Results:

Cmax-levels (plasma) of 1.01 μg Cr/g & 1.20 μg Cr/g & 4.50 μg Fe/g & 4.70 μg Fe/g were noted 0 to 72 hours (tmax as range of both analytes m/f) after oral administration of 820.2 mg Chromium(III) acetate hydroxide/kg bw, for the m & f rats on day 1, resp.

Type:

absorption

Results:

Cmax-levels (plasma) of 0.00 μg Cr/g (resulting from one male) & 0.21 μg Cr/g & 5.06 μg Fe/g & 4.56 μg Fe/g were noted 0 to 48h (tmax as range of both analytes m/f) after oral administration of 1000 mg pigment/kg bw, for the m & f rats on day 1, resp..

Type:

excretion

Results:

The plasma concentrations declined post dosing with an elimination half-life ranging from 1.7 to 13.4 hours for Cr. For Fe, only the elimination half-life of one female animal was calculable (25 hours).

Details on absorption:

Cmax-levels in plasma of 0.16 μg Cr/g and 0.55 μg Cr/g and 3.44 μg Fe/g and 4.97 μg Fe/g were noted 0 to 72 hours (tmax as range of both analytes m/f) after
intravenous administration of 0.83 mg Chromium(III) acetate hydroxide/kg bw, for the male and female rats on test day 1, respectively.

Furthermore, Cmax-levels in plasma of 1.01 μg Cr/g and 1.20 μg Cr/g and 4.50 μg Fe/g and 4.70 μg Fe/g were noted 0 to 72 hours (tmax as range of both
analytes m/f) after oral administration of 820.2 mg Chromium(III) acetate hydroxide/kg bw, for the male and female rats on test day 1, respectively.

Lastly, Cmax-levels in plasma of 0.00 μg Cr/g (resulting from male animal no. 3) and 0.21 μg Cr/g and 5.06 μg Fe/g and 4.56 μg Fe/g were noted 0 to 48 hours (tmax as range of both analytes m/f) after oral administration of 1000 mg Chromium iron oxide/kg bw, for the male and female rats on test day 1, respectively.

For comparison, the average (n=30) concentration of chromium in plasma taken before exposure at t=0 h was 0.11 μg Cr/g and for iron the mean blank plasma
concentration was 3.67 μg Fe/g plasma.

Please also refer to the field "Attached background material" below.

Details on distribution in tissues:

no data

Details on excretion:

The plasma concentrations declined post dosing with an elimination half-life ranging from 1.7 to 13.4 hours for Cr. For Fe, only the elimination half-life of one female animal was calculable (25 hours).
Please also refer to the field "Attached background material" below.

Toxicokinetic parameters:

other: bioavailability

Remarks:

The relative bioavailability of orally administered pigment was calculated approx. 0.08% (Cr) in relation to a soluble Cr3+compound (Cr3(OH)2(CH3COO)7) injected i.v.. The bioavailability of Fe was not calculable.

Metabolites identified:

not specified

Details on metabolites:

no data

Bioaccessibility (or Bioavailability) testing results:

For Cr an absolute bioavailability of 0.94 %/0.56 % (mean m/f) was calculated from soluble Cr3(OH)2(CH3COO)7 following oral administration compared to intravenous administration, and a relative bioavailability of approximately 0.08% (mean f) for Cr present in the pigment.

Please also refer to the field "Attached background material" below.

LOCAL TOLERANCE (REFERENCE ITEM; INTRAVENOUS ADMINISTRATION)

None of the animals treated with a single intravenous administration of the reference item revealed any signs of local intolerance reactions at the injection sites as observed during daily visual inspections.

CLINICAL SIGNS, MORTALITY, AND BODY WEIGHT

Chromium iron oxide:

- no abnormalities were observed in behavior or external appearance for any animal treated.

- faeces of all animals were formed normally. A black discolouration was noted for the faeces of 4/5 male animals and 2/5 female animals treated with the test item approx. 8 hours after administration. This is an expected finding being attributed to the high iron content (approx. 47%) of the test item and is not an adverse effect.

- no deaths were noted.

- body weight of all animals was in the expected range on test day 1. The slight difference in the mean body weight between the test item treated group and the reference item groups on test day 1 is a coincidental effect that was due to two test item treated animals with a relatively low body weight gain during the adaptation period.

Reference item (oral administration):

- no abnormalities were observed in behavior or external appearance for any animal treated.

- faeces of all animals were formed normally.

- no deaths were noted.

- body weight of all animals was in the expected range on test day 1.

Reference item (intravenous administration):

- no abnormalities were observed in behavior or external appearance for any animal treated.

- faeces of all animals were formed normally.

- no deaths were noted.

- body weight of all animals was in the expected range on test day 1.

TEST ITEM FORMULATION ANALYSIS

Concentration of iron and chromium in application solution:

1) iron:

Nominal concentration: 582.27 mg

Actual concentration: 550.19 mg

Recovery [%]: 94.5 %

2) chromium:

Nominal concentration: 265.13 mg

Actual concentration: 238.16 mg

Recovery [%]: 89.8 %

Conclusions:

In a relative bioavailability study, the relative bioavailability of orally administered pigment was calculated approx. 0.08% (Cr) in relation to a soluble Cr3+ compound (Cr3(OH)2(CH3COO)7) injected i.v..

Executive summary:

In conclusion, the oral relative bioavailability of the pigment "Chromium iron oxide" can be assumed to be negligible. The relative bioavailability of orally administered pigment was calculated approx. 0.08 % (Cr) in relation to a soluble Cr³⁺compound (Cr₃(OH)₂(CH₃COO)₇) injected i.v..

Reference 4

Endpoint:

basic toxicokinetics, other

Remarks:

mass balance

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015-02-06 to 2015-02-09

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Objective of study:

other: mass balance

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Version / remarks:

2010-07-22

Deviations:

no

Principles of method if other than guideline:

Groups of 5 male and 5 female Crl:CD(SD) rats were dosed orally with a single administration of chromium iron oxide, vehicle (0.8 % aqueous hydroxyl propyl methylcellulose gel), or reference item (chromium (III) acetate hydroxide) via gavage. Clinical signs, mortality and body weight were recorded. Furthermore, urine and faeces of all animals were collected in metabolic cages after administration (sampling period: 0 - 24 hours, 24 - 48 hours, and 48 - 72 hours). Lastly, gross pathology was conducted and organ weights were determined.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2014-05-14

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: at room temperature, kept dry, and stored in a tightly closed container

Radiolabelling:

no

Species:

rat

Strain:

other: Crl:CD(SD)

Details on species / strain selection:

The species was selected for this study design because the rat is a commonly used rodent species for toxicity studies.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Germany GmbH, Sandhofer Weg 7, 97633 Sulzfeld, Germany
- Age at dosing: males: 49 days; females: 53 days
- Weight at dosing: males: 248.8 - 266.6 g; females: 195.7 - 220.4 g
- Housing (exception: sampling period): kept singly in MAKROLON cages (type III plus) with a basal surface of approx. 39 cm × 23 cm and a height of approx. 18 cm; bedding material: granulated textured wood (Granulat A2, J. Brandenburg, 49424 Goldenstedt, Germany)
- Diet (ad libitum): commercial ssniff® R/M-H V1534 (ssniff Spezialdiäten GmbH, 59494 Soest, Germany)
- Water (ad libitum): drinking water
- Acclimation period: 9 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22°C ± 3°C (maximum range)
- Relative humidity: 55% ± 15% (maximum range).
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

other: chromium iron oxide: 0.8 % aqueous hydroxyl propyl methylcellulose gel; reference item (chromium (III) acetate hydroxide): water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
1) Chromium iron oxide
The test item formulation was freshly prepared on the administration day by dissolving the test item in the vehicle to the appropriate concentration. During and after preparation the formulation was stirred and the homogeneity of the suspension was checked by visual appraisal.
Administration volume: 10 mL/kg bw
The administration formulations were continuously agitated by stirring throughout the entire administration procedure.
The amount of the test and reference item was adjusted to the animal's current body weight on the administration day.

2) Reference item (chromium (III) acetate hydroxide; purity: 23.7 %):
The reference item formulation was freshly prepared on the administration day by dissolving the reference item in the vehicle to the appropriate concentration. During and after preparation the formulation was stirred and the homogeneity of the suspension was checked by visual appraisal.
Administration volume: 10 mL/kg bw
The administration formulations were continuously agitated by stirring throughout the entire administration procedure.
The amount of the test and reference item was adjusted to the animal's current body weight on the administration day.

Duration and frequency of treatment / exposure:

single administration

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose / concentration:

5 males / 5 females

Control animals:

yes, concurrent vehicle

Positive control reference chemical:

none

Details on study design:

- Dose selection rationale: The dose levels for this study have been selected after consultation with the Sponsor based on available toxicity data:
The oral LD50 value for the reference item was as follows:
chromium acetate, basic: > 5,000 mg/kg bw
Furthermore, oral bioavailabilities of soluble Cr(III) substances are given in the public domain with approx. 0.1 - 2%.

The test item oral dose of 1000 mg/kg bw corresponds to the limit dose used in a separate 28-day oral toxicity study, which is considered the maximum feasible dose. Based on the chemical composition of the test item, a dose of 1000 mg chromium iron oxide/kg bw equates to a dose of 212.1 mg Cr/kg bw (corresponding to 820.2 mg Cr3(OH)2(CH3COO)7/kg bw).

The dose level for the reference item was confirmed in two preliminary experiments employing two animals each (please also refere to IUCLID Section 7.1.1: k_Leuschner_2017_ in vivo). In the first preliminary experiment, both animals were treated once orally with 820.2 mg chromium(III) acetate hydroxide/kg bw and revealed slight pilo-erection starting approx. 15 minutes p.a. lasting for 4 hours. In the second preliminary experiment, both animals were treated once orally with 400 mg chromium(III) acetate hydroxide/kg bw No signs of toxicity were noted.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine and faeces
- Time and frequency of sampling: all animals of the test item, vehicle and reference item groups were scheduled for urine and faeces sampling. After the single administration, the animals were kept in metabolism cages. Urine and faeces were collected in 3 fractions/animal (sampling periods: 0 - 24 hours, 24 - 48 hours, and 48 - 72 hours).
The urine and faeces weight per collection fraction and animal were determined upon removal of the sample fraction.
All samples were frozen at -20°C or colder and stored at this temperature until analysis.

OBSERVATIONS
- clinical signs: before and after dosing as well as regularly throughout the working day (7.30 a.m. to 4.30 p.m.) and on Saturdays and Sundays (8.00 a.m. to 12.00 noon; final check at approx. 4.00 p.m).
- mortality: early in the morning and again in the afternoon of each working day as well as on Saturdays and Sundays (final check at approx. 4.00 p.m).
- body weight: at the time of group allocation and on the day of administration

GROSS PATHLOLOHY / HISTOPATHOLOGY
- Necrospy and macroscopic inspection: on test day 4 (approx. 72 hours after the administration) the animals were dissected.
The animals were sacrificed, weighed, dissected, and inspected macroscopically.
All superficial tissues were examined visually and by palpation and the cranial roof removed to allow observation of the brain, pituitary gland, and cranial nerves. After ventral midline incision and skin reflection all subcutaneous tissues were examined. The condition of the thoracic viscera was noted with due attention to the thymus, lymph nodes and heart.
The abdominal viscera were examined before and after removal; the urinary bladder was examined externally and by palpation. The gastro-intestinal tract was examined as a whole. The stomach and caecum were incised and examined. The lungs were removed and all pleural surfaces examined under suitable illumination. The liver and the kidneys were examined. Any abnormalities in the appearance and size of the gonads, adrenal glands, uterus, intraabdominal lymph nodes, and accessory reproductive organs were recorded.

The weight of the following organs was determined: adrenal gland (2), brain, heart, kidney (2), liver, lungs, lymph nodes (cervical (1), mesenteric (1)), ovary (2), pituitary, prostate, spleen, testicle (2), thymus, and thyroid (1) (including parathyroids).
Paired organs were weighed individually and identified as left or right.

TEST ITEM FORMULATION ANALYSIS
Remaining administration solution (approx. 5 mL) of the test item was stored at ≤- 20°C until analysis (Number of samples: 1).

Statistics:

The test item-treated and reference item-treated groups were compared statistically to the vehicle control group.
The following statistical method was used:
Multiple t-test based on DUNNETT, C. W. New tables for multiple comparisons with a control. Biometrics, 482-491 (Sept 1964): body weight / relative and absolute organ weights (p ≤ 0.01 and p ≤ 0.05)

Preliminary studies:

Please refer to the field "Details on study design" above.

Details on absorption:

Urinary excretion for all elements was negligible and below 0.00009% for Cr, and <0.0024% for Fe. Absorption rate - oral: 0.01 %.

Details on excretion:

Animals that received 1000 mg pigment /kg bw excreted 89.11% Cr and 94.1% Fe of the administered dose via urine and faeces during the first three days after exposure (mean for 10 animals). Within the first 24 hours approximately 85.82% of Cr, and 92.4% of Fe were excreted via faeces as largest fraction. Further 3.04% and 0.25% (Cr), and 0.3% and 1.5% (Fe) were excreted via faeces on the second and third day.
Urinary excretion for all elements was negligible and below 0.00009% for Cr, and <0.0024% for Fe.

CLINICAL SIGNS, MORTALITY, BODY WEIGHT, GROSS PATHOLOGY

Vehicle control group:

- no signs of systemic intolerance was observed

- faeces of control animals were normally formed.

- none of the rats died prematurely.

- individual body weights ranged from 253.4 to 260.3 g for the males and from 195.7 g to 218.2 g for the females on test day 1 and were within the expected range

- no influence was noted on the body weight at autopsy.

- no pathoplogical findings were recorded.

Chromium iron oxide:

- none of the rats treated with the test item showed any changes in behaviour or external appearance.

- faeces of control animals were normally formed.

- none of the rats died prematurely.

- individual body weights ranged from 255.8 to 266.6 g for the males and from 195.7 g to 220.4 g for the females on test day 1 and were within the expected range

- no influence was noted on the body weight at autopsy.

- no test item-related changes were noted for the animals treated with the test item at macroscopic inspection at necropsy.

- no test item-related changes in relative and absolute organ weights were noted for the animals treated with the test item.

- statistically significant differences in organ weights compared to vehicle control group which are not considered to be test item-related are as follows:

females (test day 4): increased relative thymus weight and increased absolute thymus weight (p ≤ 0.01)

males (test day 4): increased absolute left testis weight, increased absolute heart weight, and increased absolute pituitary weight (p ≤ 0.05)

 

Reference item:

- none of the rats treated with the reference item showed any changes in behaviour or external appearance.

- faeces of control animals were normally formed.

- none of the rats died prematurely.

- individual body weights ranged from 248.8 to 258.2 g for the males and from 196.7 g to 216.1 g for the females on test day 1 and were within the expected range

- no influence was noted on the body weight at autopsy.

- no reference item-related changes were noted for the animals treated with the reference item at macroscopic inspection at necropsy. An enlarged left thyroid was noted for one female animals (not considered reference item-related).

- no reference item-related changes in relative and absolute organ weights were noted for the animals treated with the reference item.

- statistically significant differences in organ weights compared to vehicle control group which are not considered to be reference item-related are as follows:

males (test day 4): increased relative thyroid / parathyroid weight and increased absolute thyroid / parathyroid weight (p ≤ 0.05)

Conclusions:

The mass balances for Cr and Fe are essentially complete and indicate that the elements contained in the pigment "Chromium iron oxide", present as Cr3+and Fe3+, are not absorbed in the gastrointestinal tracts to any significant extent, but pass the animal effectively unchanged. 

Executive summary:

Animals that received 1000 mg pigment /kg bw excreted 89.11% Cr and 94.1% Fe of the administered dose via urine and faeces during the first three days after exposure (mean for 10 animals). Within the first 24 hours approximately 85.82% of Cr, and 92.4% of Fe were excreted via faeces as largest fraction. Further 3.04% and 0.25% (Cr), and 0.3% and 1.5% (Fe) were excreted via faeces on the second and third day.

Urinary excretion for all elements was negligible and below 0.00009% for Cr, and <0.0024% for Fe.

The mass balances for Cr and Fe are essentially complete and indicate that the elements contained in the pigment "Chromium iron oxide", present as Cr³⁺and Fe³⁺, are not absorbed in the gastrointestinal tracts to any significant extent, but pass the animal effectively unchanged. 

Description of key information

The in-vitro and in-vivo experiments described above are in very good agreement with regards to the negligible level of bioavailability of the elements Cr and Fe contained in the pigment.

 

(1)   In in-vitro dissolution experiments in five different artificial physiological media, dissolved Cr and Fe concentrations were below 18 µg/L even at the highest loading of 0.1g/L, corresponding to a solubility of 0.018 %.

(2)   In a 28-day oral toxicity study with 1,000 mg/kg pigment no increase in Cr and Fe plasma and urine concentrations were observed when sampled at the end of the 28-day exposure period. From a final dose of 1,000 mg/kg of the pigment that the animals received on the last day of the study, only cumulated relative amounts of < 0.0025 % (m/f) were found in the terminal 24-h urine collection period.

(3)   In a mass balance study with a single oral dose of 1,000 mg/kg of the pigment, 89.1% Cr, and 94.1% Fe of the dose were excreted via faeces within 3 days, with only <0.0024% of the dose being excreted via urine at the same time.

(4)   In a relative bioavailability study, the relative bioavailability of orally administered pigment was calculated 0.08% (Cr) in relation to a soluble Cr³⁺compound (Cr₃(OH)₂(CH₃COO)₇)injected i.v..

Comparing the findings of in-vitro dissolution testing (1) with in-vivo results (2-4), the in-vivo data consistently demonstrates slightly lower bioavailability. This is in agreement with the general understanding that in-vitro experiments in simulated gastric juice provide a conservative estimate of actual (in-vivo) bioavailability.

 

In conclusion, the oral relative bioavailability of the pigment "Chromium iron oxide" can be assumed to be negligible, as demonstrated in three independent in-vivo studies in rats yielding very comparably results supported by an in-vitro dissolution experiment in five different artificial physiological media.

 

A rounded value of <0.01% for oral absorption can be taken forward from (i) terminal urine/plasma sampling in a study involving 28 repeated oral doses of 1,000 mg pigment/kg bw/d (<<0.008% for both metals) and (ii) a mass balance study involving a single dose of 1,000 mg pigment/kg bw (0.00009% for Cr, and <0.0024% for Fe).

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

The toxicity data in this registration dossier refer explicitly to the pigment Chromium iron oxide and document its negligible bioavailability and the complete lack of any human health hazard. Experiments on the bioavailability of the pigment are summarised and discussed in this section.

 

Summary of in-vitro bioaccessibility experiments (Pardo Martinez, 2010)

The chemical and physiological properties of the pigment chromium iron oxide are characterised by inertness because of the specific synthetic process (calcination at high temperatures, approximately 1000 °C), rendering the substance to be of a unique, stable crystalline structure in which all atoms are tightly bound and not prone to dissolution in environmental and physiological media. This manufacturing process leads to a very low bioaccessibility of the elements contained in the pigment. This has been investigated experimentally in vitro by simulating dissolution under physiological conditions considered to mimic the most relevant mexposure routes (oral, dermal and inhalation), as follows:

 

1.) Gamble’s solution (GMB, pH 7.4) which mimics the interstitial fluid within the deep lung under normal health conditions,

2.) Phosphate-buffered saline (PBS, pH 7.2), which is a standard physiological solution that mimics the ionic strength of human blood serum,

3.) Artificial sweat (ASW, pH 6.5) which simulates the hypoosmolar fluid, linked to hyponatraemia (loss of Na+ from blood), which is excreted from the body upon sweating,

4.) Artificial lysosomal fluid (ALF, pH 4.5), which simulates intracellular conditions in lung cells occurring in conjunction with phagocytosis and represents relatively harsh conditions and

5.) Artificial gastric fluid (GST, pH 1.5), which mimics the very harsh digestion milieu of high acidity in the stomach.

The dissolution of chromium of the test item chromium iron oxide is in most cases 1 µg/L or below the L.O.D at a loading of 0.1 g/L after 2 and 24 hours. Only in artificial gastric fluid (pH 1.5) a low concentration of 1.2 µg/L after 24 hours is dissolved.

 

The dissolution of iron of the test item chromium iron oxide is in a range of below the L.O.D. (pH 7.4) and 17.5 µg/L (pH 1.5) at a loading of 0.1 g/L after 2 and 24 hours. A pH dependent dissolution can be observed. In conclusion, since the dissolved Cr and Fe concentrations were below 18 µg/L even at the highest loading of 0.1 g/L, referring to a solubility of 0.018 %, this pigment may reasonably be considered biologically inert.

 

Toxicokinetic screening data from a 28 day repeated dose oral toxicity study (Leuschner, 2017)

In a 28 day repeated dose toxicity study, male and female rats were given a daily dose of the pigment "Chromium iron oxide" of 1,000 mg/kg bw/day via gavage. Individual urine samples were collected from all animals prior to sacrifice in one cumulated 24-h fraction/animal after the last oral application, and blood samples were collected from each animal upon sacrifice. The plasma and urine samples were analysed for total chromium and iron content.

 

The uptake of chromium and iron during a 24 hour urine and plasma sampling period was demonstrated to be negligible considering that <<0.00005 of the dose was excreted via urine for both metals, mirrored by either minimal or no increases in blood plasma concentrations.

The chromium and iron concentrations of the 24 h-urine samples, collected during the day before final sacrifice, ranged from: 5.87 - 134.17 μg/L urine(mean: 47.2 ± 53.2) and 3.16 - 18.3 μg/L urine(mean: 10.3 ± 7.30) for Cr and from 36.9 - 77.6 μg/L urine (mean: 49.5 ± 16.4) and 33.3 - 70.6 μg/L urine (mean: 45.6 ± 15.3) for Fe for the male and female animals of the control group, respectively.

 

For the dosed group, the concentrations were 2.38 - 823 μg/L urine (mean: 169 ± 366) and 2.66 - 13.1 μg/L urine (mean: 5.47 ± 4.44) for Cr and 25.6 - 88.1 μg/L urine (mean: 45.0 ± 25.1) and 31.1 - 61.0 μg/L urine (mean: 47.1 ± 11.0) for Fe for the male and female animals, respectively.

Following a subtraction of the background urinary element excretion (control group), and taking into account the excreted urine volume (mean 12.1 mL (m) and 8.5 mL (f)) and the body weight of the animals at the end of the study (mean 338.9 g (m) and 223.1 g (f)), the following conclusion can be made:

 

From a final dose of 1,000 mg/kg of the pigment that the animals received on the last day of the study, only cumulated relative amounts of 0.0022 % (m) or 0.00005 % (f) were found in the terminal 24-h urine collection period.

 

Summary of comparative Mass-Balance Study (Leuschner 2018a):

In a comparative mass balance study involving oral dosing of (i) the inorganic pigment "Chromium iron oxide" and (ii) a soluble salt of the element contained therein (Cr³⁺), the gastrointestinal absorption as well as urinary and faecal excretion were compared, plus consideration of dietary „background“ intake/excretion via a vehicle-dosed control. For details, please refer to the corresponding robust study summary.

In brief, 10 (5m/5f) animals per group received a single oral dose of 1000 mg/kg of the pigment or 820.2 mg Cr₃(OH)₂(CH₃COO)₇/ kg bw (corresponding to 212.1 mg/kg Cr). A third group served as vehicle treated control. Animals were individually housed in metabolic cages and daily samples of urine and faeces were collected for three days. All samples were analysed for chromium. The averaged “background” excretion via urine and faeces of the control animals was subtracted from the amounts excreted by the dosed animals, and a mass balance was calculated.

Animals that received a 212.1 mg Cr/Kg bw (administered as Cr₃(OH)₂(CH₃COO)₇ excreted 83 % (Cr), of the administered dose (as mean, male and female animals) via urine and faeces during the first three days after exposure.

The largest fraction (78.92 % for Cr) was excreted via faeces and urine (0.35 % for Cr) already within the first 24 h.

Approximately 17 % of the administered dose for Cr remain unaccounted for in this group. Due to the fact that Cr³⁺ has a very low absorbance ability within the g.i. tract (~0.1-2 %) a hypothesis that this fraction was contained in the exsanguinated blood of the animals or has distributed to the organs seems not appropriate. It may be considered that delayed excretion of the whole dose is reasonable since at 72h still ~0.32 % of the Cr dose (mean, mainly female animals) was excreted.

 

Further it may be considered that the actually received dose did not fully correspond to the nominal dose as calculated. These aspects were not further addressed within the context of this study.

 

Animals that received 1000 mg pigment /kg bw excreted 89.11 % Cr and 94.1 % Fe of the administered dose via urine and faeces during the first three days after exposure (mean for 10 animals). Within the first 24 hours approximately 85.82 % of Cr, and 92.4 % of Fe were excreted via faeces as largest fraction. Further 3.04 % and 0.25 % (Cr), and 0.3 % and 1.5 % (Fe) were excreted via faeces on the second and third day.

Urinary excretion for all elements was negligible and below 0.00009 % for Cr, and <0.0024 % for Fe.

In total, the mass balances for Cr and Fe are essentially complete and indicate that the elements contained in the pigment "Chromium iron oxide", present as Cr³⁺and Fe³⁺, are not absorbed in the gastrointestinal tracts to any significant extent, but pass the animal effectively unchanged. 

 

Summary of relative bioavailability study (Leuschner 2018b):

A relative bioavailability study involving serum kinetics over a period of 72 hours p. a. involving an i. v. dosing of a soluble Cr reference substance (Chromium(III) acetate hydroxide) compared to single oral doses of the same substance and the pigment was performed. For details, please refer to the corresponding robust study summary. In brief, 10 animals (5m/5f) per group received single doses of (1) 0.83 mg/kg Cr₃(OH)₂(CH₃COO)₇ intravenously, (2) of 820.2 mg/kg Cr₃(OH)₂(CH₃COO)₇ via oral gavage, and (3) 1000 mg/kg of the pigment via oral gavage.

Blood samples were taken at 0, 1, 2, 4, 8, 12, 24, 48 and 72 hours post exposure and blood plasma samples were prepared and analysed for the element Cr.

C_max-levels in plasma of 0.16 µg Cr/g and 0.55 µg Cr/g were noted ~15.8 or ~2.8 hours (m/f) after intravenous administration of 0.83 mg/kg Cr₃(OH)₂(CH₃COO)₇for the male and female rats on test day 1, respectively.

Furthermore, C_max-levels of 1.01 µg Cr/g and 1.20 µg Cr/g were noted ~2, or 2.2 hours (m/f) after oral administration of 820.1 mg/kg Cr₃(OH)₂(CH₃COO)₇ for the male and female rats on test day 1, respectively.

Lastly, C_max-levels of 0.002 µg Cr/g and 0.212 µg Cr/g were noted ~4 and 16 hours (m/f) after oral administration of 1000 mg pigment/kg for the male and female rats on test day 1, respectively. For comparison, the average (n=30) concentration of Cr in plasma taken before exposure at t= 0 h was 0.142 µg Cr/g plasma.

 

Due to the very low Cr levels determined after blank subtraction, no elimination half-life could be calculated. The plasma concentrations remained more or less constant in range of the background levels during the whole measurement period.

For Cr a relative bioavailability of 0.94 % (mean m/f) was calculated from soluble Cr₃(OH)₂(CH₃COO)₇ following oral administration compared to intravenous administration, and of approximately 0.07% (mean m/f) for Cr present in the pigment.

 

In sum, experimentally determined plasma kinetic values for Cr are very consistent and the very low relative bioavailability of Cr from the pigment demonstrates that the pigment can be considered inert without any systemic hazard potential for human health.

 

Summary of lung burden analysis after 90-day inhalation (Creutzenberg, 2022)

 

Male rats were exposed to concentrations of 0.6, 2.5 and 10.02 mg chromium iron oxide/m³ air for 6 hours per day, 5 days/week for 90 days via nose-only inhalation. The lung burden and clearance with chromium iron oxide were determined 1, 28 and 90 days after the 90-day exposure period. A vehicle control group was run concurrently.

 

One day, 1 month and 3 months after end of exposure, in the low-dose groups 0.14, 0.09 and 0.04 mg/lung, in the mid-dose groups 0.53, 0.34 and 0.23 mg/lung, and in the high-dose groups 1.92, 1.97 and 0.90 mg/lung of the test item chromium iron oxide (Pigment 3) were determined, respectively. The retained masses correspond quite well to the theoretical data derived from the MMPD model prediction.

During the recovery period a retarded lung clearance was observed in the high-dose group. In contrary, in the mid- and low-dose groups a partial and a physiological lung clearance was found, respectively. This reflects well the different grade of clearance retardation due to the various lung loads.

The clearance half-times of the low concentration groups with 50 days was in the range to the physiological half-time of approx. 60 days (ECETOC, 2013), or 50.5 days (median over all 5 sub-chronic inhalation toxicity studies, low-dose animals). In the mid- and high-dose group, a half-time of 81 days was determined, being above a 1.5-fold increase as compared to the physiological values of 50.5 or 60 days. The concentration-dependent increase in clearance half-times is indicative for a poorly soluble low toxicity (PSLT) particle, which may lead to a lung overload condition, i.e. impaired clearance in which the deposited dose of inhaled PSLT in the lung overwhelms clearance from the alveolar region leading to a reduction in the ability of the lung to remove particles (Driscoll and Borm, 2020). Although the 2-fold increase in lung clearance half-time retardation has not been reached, it is assumed that chromium iron oxide still fulfils the criteria as being a PSLT and that additional concentration groups with higher exposure would not have yielded any other effects than local inflammation at presence of higher clearance-half time values.

Overall conclusion:

The in-vitro and in-vivo experiments described above are in very good agreement with regards to the negligible level of bioavailability of the elements Cr and Fe contained in the pigment.

 

(1)   In in-vitro dissolution experiments in five different artificial physiological media, dissolved Cr and Fe concentrations were below 18 µg/L even at the highest loading of 0.1g/L, corresponding to a solubility of 0.018 %.

 

(2)   In a 28-day oral toxicity study with 1,000 mg/kg pigment no increase in Cr and Fe plasma and urine concentrations were observed when sampled at the end of the 28-day exposure period. From a final dose of 1,000 mg/kg of the pigment that the animals received on the last day of the study, only cumulated relative amounts of < 0.0025 % (m/f) were found in the terminal 24-h urine collection period.

 

(3)   In a mass balance study with a single oral dose of 1,000 mg/kg of the pigment, 89.1 % Cr, and 94.1 % Fe of the dose were excreted via faeces within 3 days, with only <0.0024 % of the dose being excreted via urine at the same time.

 

(4)   In a relative bioavailability study, the relative bioavailability of orally administered pigment was calculated 0.08 % (Cr) in relation to a soluble Cr3+ compound (Cr3(OH)2(CH3COO)7) injected i.v..

 

(5) lung clearance half-time measurements in combination with the absence of local adverse effects after sub-chronic inhalation exposure in rats clearly show that Chromium iron oxide fulfils the criteria as being a poorly soluble low toxicity particle (PSLT) with no intrinsic toxicity.

 

Comparing the findings of in-vitro dissolution testing (1) with in-vivo results (2-5), the in-vivo data consistently demonstrates slightly lower bioavailability and the general inertness of the substance. This is in agreement with the general understanding that in-vitro experiments in simulated gastric juice provide a conservative estimate of actual (in-vivo) bioavailability.

In conclusion, the oral relative bioavailability of the pigment "Chromium iron oxide" can be assumed to be negligible, as demonstrated in three independent in-vivo studies in rats yielding very comparably results supported by an in-vitro dissolution experiment in five different artificial physiological media.

A rounded value of <0.01 % for oral absorption can be taken forward from (i) terminal urine/plasma sampling in a study involving 28 repeated oral doses of 1,000 mg pigment/kg bw/d (<<0.008 % for both metals) and (ii) a mass balance study involving a single dose of 1,000 mg pigment/kg bw (0.00009 % for Cr, and <0.0024 % for Fe).

Absorption rate - oral: 0.01 %